Metallurgical furnace and method of treatment of work



June 26, 1956 w. BESSELMAN EI'AL 2,752,147

METALLURGICAL FURNACE AND METHOD OF TREATMENT OF WORK Filed Dec. 21,1950 4 Sheets-Sheet 1 g Q INVENTORS b WAYNE LEO BESSELMAN t JAMES HENRYSOMERSET 5 GUSTAVE M. TAUBER W ZMM ATTO R N EYS June 26, 1956 w. L.BESSELMAN EI'AL 2,752,147

METALLURGICAL FURNACE AND METHOD OF TREATMENT OF WORK Filed Dec. 21,1950 4 sheets sheet 3 Controller L 63 L, L2

60 Inlet 56 EAux.|n|et E V V 52 A 76 2 77 58 65 Motor B Pump 6 Furnace Pas i 33 31 INVENTORS. WAYNE LEO BESSELMAN JAMES HENRY SOMERSET GUSTAVEM. TAUBER June 26, 1956- w. L. BESSELMAN ETAL 2,

METALLURGICAL FURNACE AND METHOD OF TREATMENT OF WORK Filed Dec. 21,1950 4 Sheets-Sheet 4 I N VEN TORS' WAYNE LEO BESSELMAN JAMES HENRYSOMERSET GUSTAVE M. TAUBER ATTORNEYS United States l' atent FMETALLURGICAL FURNACE AND METHOD OF TREATMENT OF WORK Wayne LeoBesselman, Philadelphia, James Henry Somerset, Glenside, and Gustave M.Tauber, Phiiadeiphia, Pa., assignors to Leeds and Northrup Company,Philadelphia, Pa., a corporation of Pennsylvania Application December21, 1950, Serial No. 201,906

14 Claims. (Cl. 266-4) This invention relates to methods of andapparatus for heat-treating work and is particularly applicable where itis desired to maintain the work under atmosphere control both during,and after completion of, the heating part of the cycle.

The present invention is particularly applicable to annealing,normalizing, hardening, case carburizing, carbon restoration, and tohomogeneous carburizing, and the heat-treating apparatus has thecapability of treating Work over the full range of normal heat-treatingtemperatures heretofore utilized.

Heretofore, efforts have been made to prevent formation of oxide orscale on the surfaces during the heat treatment of the work. To this endit has been proposed that during the heating of the work, anon-oxidizing atmosphere be maintained, as for example one with a carboncontent, and that such protective atmosphere further be maintainedduring transfer of the work from the heating chamber to the quenchingchamber. However, prior to the invention made by one of applicants andhis co-inventor, United States Letters Patent No. 2,541,857, entitledControl of Constituent-Potentials, continuous control of theconstituent-potential within a heating chamber had not beensatisfactorily attained. Advantage is taken in the present invention ofcertain features of said joint invention disclosed in said patentapplication to the end that there is not only achieved uniformity ofatmosphere within the heating chamber as regards the transference of aconstituent thereof to and from the work, but also an atmosphere ofknown and predetermined composition is maintained within a vestibule orloading chamber associated with the heating chamber, control of saidatmosphere within the vestibule being regulated by theconstituent-controlling means of the heating chamber.

Further in accordance with the present invention, whenever a door of theheating chamber is opened, there is established an auxiliary supply tothe heating chamber of constituent material which compensates for anydilution of the atmosphere of the heating chamber; but the introductionof the added constituent material may not increase theconstituent-potential of the furnace atmosphere materially above itspreselected value since the constituent-controlling means acts todecrease the supply thereof as soon as the constituent-potential withinthe heating chamber tends to rise above its selected value.

After completion of the heating step of the heat-treating cycle, thework is withdrawn through an open door of the chamber into the vestibuleor discharge chamber without encountering a change in the character ofthe atmosphere within the vestibule, which is solely dependent upon thatof the heating chamber. The work is automatically brought to rest on anelevator in position to be directly lowered into a quench tank. Whereair-temperature quenching is desired, the elevator need not be used, butwhere oil or other liquid quenching is desired, the work is immediatelylowered to a predetermined level where the elevator platform cooperateswith stationary structure 2,752,147 Patented June 26, 1956 to localizethe flow of the quenching liquid in the region of the work. Moreparticularly, a circulating pump is provided having one connection onone side of the platform support and the other connection on theopposite side, preferably the suction side of the pump being below thestationary work support for positive forced circulation of quenchingliquid intimately about the work uniformly to lower the temperaturethereof at the desired rate.

Further in accordance with the invention, there is provided ametallurgical furnace of rugged construction of relatively simple designhaving great flexibility in its operation and applications, and whichhas many features which may be usefully employed with and without otherfeatures thereof.

For further objects and advantages of the invention, reference should behad to the following description taken in conjunction with theaccompanying drawings, in which:

Fig. 1 is a side elevation partly in section of a typical metallurgicalfurnace embodying the invention, with certain associated apparatusomitted;

Fig. 2 is a front elevation of the manually operable control valve andmechanically interlocking actuating elements thereof;

Fig. 3 is a sectional view taken on the line 3-3 of Fig. 1;

Fig. 4 diagrammatically illustrates in one position a manually operablecontrol valve and associated elements of the furnace;

Fig. 5 diagrammatically illustrates the control valve of Fig. 4 in itsother control position;

Fig. 6 diagrammatically illustrates a control system of a metallurgicalfurnace as shown in Figs. 1 and 2; and

Fig. 7 diagrammatically illustrates the foot treadle controller of Fig.2 in conjunction with the associated piping for the actuating cylinders32 and 80.

Referring to the drawings, the invention in one form has been shownapplied to a metallurgical furnace 10 having a heating chamber 11, avestibule or entrance chamber 12, and a quench tank 13 having alocalized quenching zone 13a. It is believed the invention will bereadily understood by an immediate explanation of the manner in whichthe furnace is used for the treatment of work. Accordingly, it will beassumed that the furnace is in readiness for the treatment of work, thatis to say, it is up to temperature, the desired atmosphere has beenestablished in the heating chamber 11 and in the vestibule 12. Anexhaust flame 14, ignited by a pilot burner 15, consumes the gases fromthe vestibule.

The metallurgical furnace of Figs. 1 and 3 is designed for use withtrays for carrying the work, one such tray 16 being shown within theheating chamber 11. Such a tray loaded with work is first deposited on arack 17 disposed to one side of the path of a door 18 of the vestibule12, which door is supported on angle brackets 18a. In Fig. 1 the door 18is illustrated in the closed position. When swung about its pivotalmounting means or shaft 19 in a counterclockwise direction, as by handle1812, it lies between the loading rack 17 and a discharge rack 20. Thus,a tray of work can be slid directly from the loading rack 17 onto thedoor which thus serves as a transfer support for the tray as it is movedinto the vestibule 12. While in Figs. 1 and 3 there is illustrated astop element or abutment 21 in the path of the tray, such stop orabutment is, by the opening of door 18, moved out of the path of thetray by means of a bifurcated link 22 rotated by shaft 19 which operatesthrough a link 23 and a link 24 to lower the abutment out of the path ofthe tray. The link 24 is guided in its vertical movement by one or moreU-shaped clips 25. Upon opening of the door 18, the exhaust flame 14, isextinguished.

After the tray 16 and the work carried thereby is pushed into thevestibule 12, the door 18, of course, is immediately closed.

Referring to Fig. 3, it will-be seen that the shaft 19 has connected toit an actuating arm 27 which upon opening the door closes a valve 28disposed in a conduit forming a flow passage 29 interconnecting theheating chambe: 11 and the vestibule 12. Thus, while the door 18 is inthe open position, there is avoided loss of protective atmosphere withinthe heating chamber 11. However,

upon closure of door 18, the valve '28 is opened to es-' tablish forcedflow of gases from the heating chamber 11 to the vestibule 12. Themanner of producing the forced flow will be fully explained hereinafter.

Preferably, after the exhaust flame 14 is reestablished, indicating thepresence in the vestibule of the protective atmosphere, an operatoractuates a foot treadle 39 connected to a valve 31, from the positionshown in Fig. 7 to the position shown in Fig. 2'to admit fluid underpressure to an actuating cylinder 32, Figs. 1, 4 and 7 to elevate thefire door 33 illustrated in Fig. l in the closed position between theheating chamber 11 and the vestibule 12. As soon as the door 33 is inits open position, a push rod may be inserted through a relatively smallopening 34 in the door 18, normally'closed by a pivoted cover plate 180,to push the tray from the position illustrated by broken lines onelevator platform 35 in the vestibule 12 to the position illustrated inthe fire chamber 11 on the tray support 36.

It is to be observed, Figs. 2 and 7, that upon operation of the treadle30 to the position shown in Fig. 2, an,

end thereof is moved downwardly against an end of in terlock lever 37pivoted at 38 to complete a mechanical connection between treadle 30 andtreadle 40 disposed for actuation of control'valve 41 for the elevatormechanism, shown as pneumatic cylinder 80, of platform 35.

If, with treadle 36 in the actuated position to raise door 33; theoperator were to rotate treadle 40 in a. counterclockwise direction, thelever 37 would immediately actuate treadle 30 to close door 33, or ifthe operator were pressing down on treadle 30 to position shown in Fig.2, the treadle 40 could not then be rotated. An advantage of theinterlocking lever 37 is that it does not interfere with the operationof treadle 30 with the parts in the positions illustrated in Fig. 2, andneither does it interfere with the operation of treadle 40 with treadle30 in the close-door position, but it is effective to prevent operationof the elevator mechanism at any time the valve 31 of actuator 32 hasbeen actuated to the door-opening position. 7

After the work and tray 16 is in position on the tray support 36, thedoor 33 is closed by actuation of the treadle 30 from the positionillustrated in Fig. 2. As

'it is lowered, the door 33 is pressed against the outer wall 'of thefire chamber by means of cams 42 and 43 which engage pins 44 and 45extending outwardly from the sides of thedoor. As best seen in Fig. 3,the fire door 33 overlaps the opening into the heating chamber 11, andas best seen in Fig. 1, the lower face of the door 33 rests upon anextension of the floor of fire chamber 11. Thus the door forms asubstantially gas-tight seal for the fire chamber 11. After the work hasbeen retained in the heating chamber 11 for a desired length of time,determined by the nature of the treatment to which it is to besubjected, it is removed therefrom. While in the heating chamber 11, thetemperature is under the control of a thermocouple 46 mounted within athermowell 47, the thermocouple 46 being shown in Fig. 6 as connected toa temperature controller 48 which, through control of operation of acircuit-breaker 49, opens and closes a circuit from suitable supplylines 50 to control the energization of heater coils 51 disposed withinthe heating chamber 11. The temperature controller 48 may be of the typefully disclosed in United States Patent No. 2,325,232, Davis.

While electrical heating of the chamin Fig. 6 as under the control ofcontacts 62 actuated by her 11 has been illustrated, it is to beunderstood that controlled gas heating or any other suitable typeofheating can be utilized with full advantage taken of the features ofthe present invention.

It is to be observed that the heating chamber 11 is of considerablygreater length than the length of the work supporting tray '16.Preferably, it is at least half as long again as the length of the tray16. It has been found that by arranging the radiant heat-producingmeans, as the heater coils 51, along the opposite side walls of thechamber 11, both in positions opposite tray 16 and above and below it,as diagrammatically shown in- Fig. 1, radiant heat will be transferredto the work in the tray with a surprising degree of uniformity. Inaccordance with the present invention, it has been found unnecessary toprovide heat-generating devices such as electrical heating coils alongeither the front wall, the rear wall, the roof or n e fioor of theheating-chamber. Thus, there is'a'substantial saving in the cost andmaintenance of theheatingdevices by minimizing the number required, thesavings'morethan offsetting the cost'of the slightly larger size,particularly as regards length, of the heating chamber.

For a great many heat-treating operations, it is highly desirable tomaintain under accurate control the character of the atmosphere withinthe heating chamber. In accordance with the present invention,constituent forming material is supplied by way of inlet 52 fordistribution through openings 53 and a distributing plate 54'withinchamber 11.

More particularly, Fig. 6, a carburizing agent may be introduced throughinlet 52 under the control of valves 55 and 56. In practice, a motor 57driving a pump 58, preferably of the constant-head type, supplies thecarburizing agent which, when valve 56 is opened as by the coil 60,flows through throttling valve 55 and a flow indicator 61 to the inletline 52. While the throttling valve 55 is not deemed essential, it isdesirable to include-it to separate the function of regulating, as byvalve 55, the

supply of carburizing agent from the function of valve 56 in turning theflow on and off. a

The energization of the valve-operating coil is shown a controller 63which may be of the form disclosed in said Patent No. 2,541,857.Briefly, the controller may include a Wheatstone bridge, in one arm ofwhich there 7 is provided the constituent-potential sensitive elementdisposed within the furnace 10 in a position to be subjected to thefurnace atmosphere. The controller, in response to unbalance of thebridge due to change in the constituent-potential from apredetermined:selectedvalue,

functions to open and close the contacts 62 to regulate a the flow ofthe constituent-forming-material, such as a carburizlng agent, throughinlet 52 to the furnace 10.

In practice, systems will be used of the type disclosed in United StatesLetters Patent No. 2,698,222, granted uponapplication Serial No.122,946, filed October 22, 1949,

.Patent No. 2,698,222, by Raymond L. Davis II,"for

Methods of and Apparatus, for Calibrating Measuring Systems forConstituent Potentials, a co-employee of ours. Pursuant to said PatentNo. 2,698,222, the sensitive element 65 may comprise a wire having acomposition capable of reversible transference of the constituent to bemaintained at a predetermined value in. the furnace atmosphere, ascarbon or nitrogen. More particularly, the wire may comprise a length of#40 A. W. G. iron wire,

preferably the ferrous alloy described in United Patent" No. 2,325,759,Finch. The. detector and controller 63 may be either of the galvanometerand mechanical relay type such as shown in United States Patent No.1,935,732, Squibb, or it may be of the electronic type as shown inUnited States Patents Nos. 2,113,164 and 2,3 67,746, Williams. Ifmeasuring instruments of the foregoing typesare utilized, their scalesmay be calibrated in terms: of. the constituentrpotential of the furnaceatmosphere, that;

is, the transference and the possibility of transference of aconstituent of the furnace atmosphere and the work subjected thereto,which transference varies the composition of the case or near-surfaceregion of the work primarily affected by said transference.

The length of time that the tray or basket 16 and the work containedtherein remains in the heating chamber 11 and the nature of theatmosphere maintained therein will depend entirely upon the nature ofthe treating operation desired. If the treatment is solely forhardending, annealing or normalizing the controller will be set tomaintain a carbon atmosphere having a carbon potential correspondingwith that of the work. Thus, there will be avoided an increase ordecrease in the carbon content of the work, and assurance will be hadthat in the quenching the hardness acquired will be related to a knownvalue of carbon content. In the event some carbon is to be added to thework, the constituent-potential will be made somewhat higher to increasethe carbon potential of the furnace atmosphere for transference ofcarbon to the work for added carburization thereof. If there has beencarbon depletion of work, obviously it can be restored during treatmentwithin the heating chamber 11. Variable carbon content of work can bemade homogeneous. A further important advantage of the present inventionis that the carbon content can be maintained over the full range ofheat-treating temperatures utilized for a wide variety of ferrous work.

It will now be assumed that the work has been in the heating chamber 11for the requisite period of time under selected carburizing conditionand that the work is to be quenched. Accordingly, an operator depressesthe treadle 30 to its position shown in Fig. 2 to raise the fire door 33by means of the pneumatic device 32. Rotation of treadle 30 positionsvalve 31 as shown in Fig. 4 to connect a source of compressed air 66 byway of a throttling valve 67 to the lower side of a piston 68 of thepneumatic device 32. The valve 31 also connects the upper side of piston68 through a throttling valve 69 to atmosphere as through the dischargeopening 70. The piston 68 is actuated to raise the door 33. At the sametime it will be observed that air under pressure is applied as by pipe71 to a pressure-responsive device shown as a Sylphon bellows 72 whichexpands to close an electrical circuit through contacts 73 whichincreases the supply of constituent material to the chamber 11.

As shown in Fig. 6, an energizing circuit is completed from supply linesL1 and L2 by the switch 73 for the operating coil 74 of a valve 75. Thevalve 75 controls the flow of constituent material, as the carburizingagent, supplied under pressure by the pump 58 to a pipe 76, through thethrottling valve 77, a flow indicator 78, and thence by way of inletpipe 52 to the furnace 10. The relative rates of flow of the two streamsof constituentforming material are established by the setting of thethrottling valves 55 and 77. In most cases, the stream through valve 55will be small, as for example, about three pints of a carburizing liquidper hour, whereas the valve 77 will be set for a higher flow, as forexample, twenty pints of carburizing liquid per hour. Thus, theincreased supply of the carburizing agent will immediately increase thecarbon potential within the heating chamber 11 in compensation foringress into the vestibule of air due to leakage upon the opening of theclosure 180. However, the carbon potential within heating chamber 11 isnot likely to exceed the selected value by a substantial amount for thereason that during the time the door 33 is in open position, thesensitive element 65 and associated control continue to function; andwhen.

the constituent-potential rises above the selected value, the controller63 will close the valve 56 to terminate flow of the carburizing fluid byway of the flow indicator 61. By suitably adjusting the ratio of flow ofthe two streams, the carbon or constituent-potential of the furnace at.-mosphere with the door 33 open or closed may be maintained at asubstantially constant value, for example,

6 within twenty to thirty points of carbon (0.2. to 0.3 per cent carbon)in contrast with wide changes in carbon potential heretofore experiencedin furnaces to which the present invention has not been applied.

With the door 33 in the open position, a hook inserted through theopening 34 of door 18 is inserted into the opening in a handle 16a oftray 16 for withdrawal past the door 33. Since the door 18 is in closedposition, the stop 21 will be elevated as shown in Fig. 1. Accordingly,the tray 16 may be rapidly moved until it abuts against the stop 21. Atthis time the operator may operate treadle 30 to lower the door 33.Operation of treadle 30 from the illustrated position in Fig. 2 to thatin Fig. 7 completes connections through the valve 31 as shown in Fig. 5,admitting compressed air from the supply pipe 66 by way of valve 69 tothe upper part of the cylinder of pneumatic device 32, the under side ofthe cylinder within which the piston 68 is disposed then being connectedby way of valve 67 to the outlet 70. At the same time the decreasedpressure within bellows 72 opens the contacts 73 to terminate the flowof the auxiliary stream of constituent-forming material by way of supplypipe 76.

As soon as the door 33 is lowered, the operator will depress treadle 40from the illustrated position, Fig. 7, to admit air to the upper portionof a pneumatic actuator or cylinder to lower the piston rod 81 whichsupports the platform 35, Fig. l, as by the structural members 82 and83, disposed on opposite sides of guides 85 and 86, Fig. 3. The valve 41is of the same construction as valve 31 and the pneumatic actuator 80 isof the same construction as actuator 32. Thus, Figs. 4 and 5 alsodiagrammatically illustrate operation of valve 41 and of actuator 80,with an assumed omission of bellows 72. The pneumatic actuator 80 forthe platform 35 is designed to lower the tray 16 until it rests upon astationary support 84 shown in the lower portion of the quenching zone13:: within the tank 13. The bottom of the tray 16, shown in brokenlines at the bottom of the quenching zone 13a, rests upon the stationarysupport 84 to localize the flow of the quench oil through the supportingribs 16b of the tray. More particularly, a pump driven by motor 87 hasits inlet 91, Fig. 1, connected to the quenching zone 13a below thestationary support 84 and a screen 92. A valve 89, Fig. 3, in outlet 88serves to regulate the rate of flow of the quench oil or other liquidwhich may be utilized for quenching purposes. The pump 90 by withdrawingquench oil from below the screen 92, Fig. 1, produces forced and uniformdownward flow of quench oil as indicated by the arrows over and aboutthe work supported on the tray 16, uniformly and rapidly to lower itstemperature for the hardening of thework. The discharge of the pump isby way of line 88 and valve 89 to a cooler 94 disposed within quenchtank 13 outside of the quenching zone 13a. Oil is discharged from anopen end of cooler 94 into the body of quench oil, the oil level 95being somewhat higher in the cooling zone in which the cooler 94 islocated than the oil level 96 in the quenching zone, the latter beinglower by reason of the suction developed by the circulating pump 90. Itis to be observed that the quenching zone is defined by a rear wall 97common to both zones. Separate side Walls 98 and 99 extend to the bottomof the tank on opposite sides of the platform 35, and a front wall 100completes the wall structure of the quenching zone. The side walls areprovided with openings 96a and 96b for flow of quench oil into thequenching zone and downwardly about the work, the slot in wall 100through which rod 24 extends also forming an additional flow-path. Valve93 is a shut-01f valve, Fig. 3.

The cooler 94 is of conventional construction well known to thoseskilled in the art, provision being made for the circulation throughcooling coils of a cooling fluid,

such as water, admitted through a supply line under work.

the control. of a, valve 111 operablebya coilor solenoid 112; Thesolenoid 11-2.may'be energizediunder thereon. trol of a-controller 115whichalsocontrols the operation ofa circuit breaker 116 which controlsthe energization of an. immersion heater 117. Such-acombined controlsystem. maybe of the type fully described in United States Patent No.2,530,326, Davis. The coolingv liquid from the cooler 94 is dischargedby wayofoutletpipell'll;

Under the control of aresistancethermometer 114 or other typeoftemperature sensitive device extendinginto well 114:: of pump intakeIine=9 1, the controller 115 of the type shown in saidDavis Patent-2,'530,326, functions to maintain the temperaturcof thequenchi'ngliquid,as oil, at a predetermined value. For example, when it is below aselected temperature, current'from supply lines Lt 1nd Lz issupplied bycontroller 115 to the circuit breaker 316 and to the immersion heater11-? to raise the temperature of the'quenching-liquid to itsselected'value;

However, when theheat-of the work elevates the temperature of thequenching liquid above the selected value,

the controller 115 by way of lines 118 energizesthe coil 15.2toopenvalve 111 for admission of cooling liquid-to the cooler 94.

After completion of the quenching of the work, the operator will depressthe treadle 40'to moveit to the position shown in Fig. 2 to raise theelevator preparatoryto discharge of the Work from the vestibule 12. Itis to be observed the operator could not raise'the door 33 during thetime the elevator or'plat-form 35- was in its lowermost position byreason of the interlock lever 37 which would have prevented thatoperation.

With the elevator inthe raised position, the door 18 is opened, thestop- 21 then being moved outof the path of tray 16 and it is thenwithdrawn through the door and slid to the discharge rack 20. The rack20 is elevated somewhat above a drip pan 101 having openings 101aleading into the quench tank. Thus, oil draining from the tray and thework isreturned to the quench tank.

it is to be understood the foregoing operations will be repeated forsuccessive charges of work and that the output of the furnace willremain at a high level of chiciency due to the fact that nosubstantialtime; is lost in maintaining the needed protective atmospherefor the In particular, the carbon potential of-the heating chamber 11 ismaintained at substantiallyitsdesired value at all times. The auxiliarysupply of constituent-forming material initiated each time the door 33is opened insures a rise in the constituent-potential of the gaseswithin the heating chamber 11, andthus during the charging of the firechamber, as by transfer of the work tray 16 either from the loadingplatform directly to the fire chamber or by transfer first to thevestibule and later to the fire chamber, assurance is'had that the workwill be under a protective atmosphere, an atmosphere which Will'at alltimes be near the selected value of constituent-potential. A furtherimportant function of the auxiliary supply ofconstituent-formingmaterihl is the protection of the sensitive element65- which, it will be recalled, is of relatively fine wire. Hence, itscross-sectional area must not be changed as would occur if it weresubject to oxidizing conditions. The resulting change in resistancewould greatly interfere with its operation in the control of theconstituent-potential. However, by maintaining theeonstituent-potentia-l within the heating, chamber at a relatively highlevel, the sensitive element 65 is protected and it continues tofunction during run after run with great accuracy.

While a separate fan or air pump may be utilized to withdraw gases fromthe heating chamber 11', and ad'- vantage taken of certain features ofthe present invention, considerable savings may result by utilizingthefan 102 located within thefire chamber 11 and driven by a motor 193located outside that chamber, It is preferred that the fan lit-2 bedisposed within a housing which includes a plurality of vanes extendingsubstantially tangent to the the work supported in the tray 16.

A detailed disclosure of the fan and the preferred associated vanes isset forth in United States Letters Patent No. 2,686,665 granted uponcopending application Serial No. 190,152, filed October 14, 1950, by oneof us and .l. J. Schultz," a co-employee of ours, for'Heat-TreatingFurnace.

Advantage is taken of the fact that zones of high pressure. are producedby a fan, as. at certain of the adjacent directing vanes, that'is,pressures higher than in other portions of the heating chamber 1-1. Bydisposingvthe inlet 29a of recirculating pipe/29 in a high pressurezone: adjacent the fan 102, there will be forced circulation of gasesfrom the heating chamber 11 into the vestibuleof loading chamber izsolong as the door 13 isclosed, the

condition required for the valve 28 to be in the open position. In thismanner thereis. avoided the need of an additional motor and fan forwithdrawing the gases from the heating zone for supply to thevestibule-12. In this. connection, it is to be observed that gases fromthe heating chamber 11 are not returned thereto but form the supply ofthe gases for the exhaust flame 14. As shown,

the inlet 29a is in the form of a scoop, this being preferredwhere thedirecting vanes are notprovided.

While'a preferred embodiment of the invention has been set forth, it isto beunderstood that modifications may bemade, certain features usedwithout other features, and that other modifications may be made withinthe scope of the appended claims.

What is claimed is:

l. A heat-treating furnace having a heating chamber and a vestibuleforreceiving work preparatory to' delivery into said heating chamber, a fandisposed within said heating chamber having a high-pressure zone forforced circulation of gases withi-n'said heating chamber, walls forminga flow passage extending between said heating chamber and said vestibulewith an entrance portion extending into said'heati-ng chamber to a pointwithin saidhigh-pressu-re zone and adjacent said fan portion extendinginto said heating chamber to a point for forced flowinto said heatingchamber and for receiving the. work said vestibule to form an atmospherein said. vestibule and extending to the liquid level of said tank, saidatmosphere having substantially the same'constituent quality as thatwithin said heating chamber, and means including a constituent-sensitivedevice exposedjto the atmosphere of'said.

. heating chamber for controlling the constituent concentration in saidheating chamber and of the atmosphere in said vestibule formed by thegases transferred thereto from said chamber.

3. A heat-treating furnace having a heating chamber and a vestibule forreceiving work preparatory to delivery 9 into said heating chamber, adoor between said chamber and said vestibule, a fan disposed tocirculate gases within said heating chamber, a flow passage between saidheating chamber and said vestibule for transfer of gases from saidheating chamber to said vestibule with said door in open or in closedposition to form an atmosphere in said vestibule having substantiallythe same constituent quality as that within said heating chamber, theinlet to said passage being disposed inwardly of said chamber and withina hi h-pressure zone adjacent to, and produced by, said fan, a valve insaid flow passage for regulating the rate of flow of gases therein,means including a constituent-sensitive device exposed to the atmosphereof said heating chamber for controlling the constituent concentration insaid heating chamber and of the atmosphere in said vestibule formed bythe gases transferred thereto from said chamber, said vestibule havingan access door movable between closed and open positions for placingwork within said vestibule, and means operable upon movement of saidaccess door towards open position to close said valve at times when saidfirst-named door is in closed position.

4. In combination, a heat-treating furnace having a heating chamber, anormally closed vestibule adjacent said heating chamber, a door movablebetween open and closed positions to establish communication betweensaid vestibule and said heating chamber, supply means for delivering tosaid heating chamber a constituent material for maintaining theconstituent-potential of the atmosphere within said heating chamber at apredetermined value, means responsive to change in theconstituentpotential of said atmosphere for regulating control of saidconstituent supply means to maintain said constituentpotential at saidpredetermined value, means forcibly circulating gases from said heatingchamber to said vestibule to maintain therein an atmosphere whoseconstituent content is under the control of said constituent-potentialresponsive means, and means operable upon opening of said door of saidheating chamber for establishing an auxiliary supply of said constituentmaterial to said heating chamber.

5. in combination, a heat-treating furnace having a heating chamber, anormally closed vestibule adjacent said heating chamber, a door movablebetween open and closed positions to establish communication betweensaid vestibule and said heating chamber, supply means for delivering tosaid heating chamber a constituent material for maintaining theconstituent-potential of the atmosphere within said heating chamber at apredetermined value, means responsive to change in theconstituentpotential of said atmosphere for regulating control of saidconstituent supply means to maintain said constituent-potential at saidpredetermined value, means forcibly circulating gases from said heatingchamber to said vestibule to maintain therein an atmosphere formed bygases transferred from said chamber whose constituent content is underthe control of said constituent-potential responsive means, and meansoperable upon opening of said door of said heating chamber forestablishing an auxiliary supply of said constituent material to saidheating chamber while said door is in its open position, saidconstituent-potential responsive means functioning to decrease deliveryof said constituent material by said supply means when theconstituent-potential within said furnace exceeds said predeterminedvalue.

6. In combination, a heat-treating furnace having a heating chamber, avestibule adjacent said heating chamber, a door movable between open andclosed positions to establish communication between said vestibule andsaid heating chamber, supply means for delivering to said heatingchamber a constituent material for maintaining the constituent-potentialof the atmosphere within said heating chamber at a predetermined value,means responsive to change in the constituent-potential of saidatmosphere for regulating control of said constituent supply means tomaintain said constituent-potential at said predetermined value, meansforcibly circulating gases from said heating chamber to said vestibuleto maintain therein an atmosphere formed by gases transferred from saidchamber whose constituent content is under the control of saidconstituent-potential responsive means, means operable upon opening ofsaid door of said heating chamber for establishing an auxiliary supplyof said constituent material to said heating chamber while said door isin its open position, said constituent-potential responsive meansfunctioning to decrease delivery of said constituent material by saidsupply means when the constituentpotential within said furnace exceedssaid predetermined value, and flow regulating means for regulating themaximum rates of flow from said supply means and from said auxiliarysupply to establish maximum predetermined rates of flow when said dooris in said open position.

7. The method of maintaining substantially constant the constituentconcentration within a heating chamber during the transfer of work toand from the chamber, which comprises regulating the flow to the chamberof a first stream of constituent-forming material to maintain theconstituent-potential within the chamber at a selected substantiallyconstant value, increasing the supply of said constituent-formingmaterial by initiating flow of a second stream of said material duringtransfer of work to and from the heating chamber, and decreasing theflow of said first stream of constituent-forming material when saidsecond stream increases the constituent-potential of the atmosphereabove said selected value.

8. The method of maintaining substantially constant the constituentconcentration within a heating chamber and within a vestibule during thetransfer of work between said vestibuie and said heating chamber, whichcomprises regulating the flow to the chamber of a first stream ofconstituent-forming material to maintain the constituent-potentialwithin the chamber at a selected value, forcibly flowing a stream ofgases from said chamber to said vestibule for producing therein anatmosphere having the constituent concentration therein incorrespondence with that of said chamber, increasing the supply of saidconstituent-forming material by initiating the flow into said chamber ofa second stream of said material during transfer of work to and from theheating chamber, and decreasing the flow of said first stream ofconstituent-forming material when the constituent-potential of theatmosphere within said heating chamber rises above said selected value.

9. The method of heat-treating work under conditions of a controlledconstituent concentration of an atmosphere with transfer of said work toa quenching medium While under the protection of said atmosphere, whichcomprises heating the work within a heating chamber, supplying to thechamber a constituent material to establish an atmosphere having aselected concentration of said constituent therein, regulating thesupply of said material in response to change of theconstituent-potential of said atmosphere from a predetermined selectedvalue, forcibly removing gases from said heating chamber to maintainwithin a discharge chamber an atmosphere having a constituentconcentration dependent solely upon that maintained with in said heatingchamber, during transfer of said work from said heating chamber to saiddischarge chamber establishing an auxiliary supply of theconstituent-forming material to the heating chamber, and decreasing thefirst-mentioned supply of said material when said constituent-potentialwithin said heating chamber exceeds said selected value.

10. A heat-treating furnace having a heating chamber and a vestibule forreceiving work preparatory to delivery into said heating chamber, a fandisposed adjacent the floor of said chamber to produce a region ofpressure at the periphery higher than at the central part to circulategases forcibly in a closed path within said heating chamber, a conduitforming a flow passage having an inlet, opening intosaidv peripheralzone and adjacent thereto and eXtend-ingbetween and in-part outside ofsaid heating; chamber and of said vestibule with an inlet opening intosaidxvestibule for forcible transfer of gases from saidheating chamberto said vestibule to form an atmosphere therein having substantially thesame quality as that within said heating chamber, and a Work supportwithin said vestibulebelow the zone of entry of said gases.

1]. In combination, a heat-treating furnace having a heating; chamber, adoor providing access to said heating chamber, a vestibuleadjacent saiddoor forming a closed loading; chamber, a closure for said vestibulemovable between open and closed positions, a quench tank disposed belowsaidvestibule, an elevator for supporting work within said vestibule fortransfer to and from said heating chamber, elements disposed within thepath of work moved-from said chamber to said vestibule to position' saidWork on: said elevator When, said closure is in its, closed position andoperable out of the path of said work when'said closure is in its openposition.

12. Aiheat-treating furnace having a heating chamber and a vestibule forreceiving Work preparatory to delivery into said heating chamber, a doorbetween said vestibule and said chamber, afan disposed to circulategases within said heating chamber, a flow passage between said heatingchamber and said vestibule for transfer of gases from said heating;chamber to said vestibule with said door in open or in closed positionto form an atmosphere in said vestibulehaving substantially the sameconstituent quality as that within said heating chamber, a valve in saidflow passage for regulating therate of flow of gases therein, saidvestibule having an access door movable between closed and openpositions for placing Work within said vestibule, and means operableupon movement of said access door towards open position to close saidvalve to prevent flow of furnace gases'to said vestibule from saidfurnace while said access door is open and said firstnamed door isclosed,

13. A metallurgical furnace comprising a heating chamber,a vestibule forreceiving work moved into and out of, said heatingtchamber, a quenchtank disposed below said vestibule, an elevator for lowering Work intoand out of said, quench tank, a door for said heating chamber, actuatingmechanism for said door and for said elevator,

' means for controlling, said actuating mechanism to raise and lowersaid elevator at will while said door is closed, means for controllingsaid actuating mechanism to raise and lower said door. at will when saidelevator is in its uppermost position, means forpreventing opening ofsaid door and for maintaining it closed when said elevator is in itslowermost position in said quench tank, and means for preventinglowering of said elevator while said door is in its open position.

14. The combination set forth in claim 13 in which said means foractuating said elevator and for actuating said door respectivelyincludes a door treadle and an elevator treadle each pivoted formovement between valveopening and valve-closing positions, and a pivotedlever having its ends movable respectively to positions within the pathof each of said treadles for preventing operation of said door treadlefor opening of the door when the elevator is in its lowermostpositionand for preventing operation of said elevator treadle when said door isin its open position.

References Cited in the file of this patent UNITED STATES PATENTS890,250 Thompson June 9, 1898 890,251 Thompson June 9, 1898 786,365Kenworthy Apr. 4, 1905 1,713,136 Leek May 14, 1929 1,742,739 UrschelJan. 7, 1930 1,808,241 Martin June 2, 1931 1,851,831 Hayes Mar. 29, 19321,940,948 Harsch Dec. 26, 1933 1,999,757 Harsch Apr. 30, 1935 2,064,532Gilbert Dec. 15, 1936 2,223,603 Darrah Dec. 3, 1940 2,307,005 Ruben Dec.29, 1942 2,307,522 Mahin Jan. 5, 1943 2,394,002 Ness Feb. 5, 19462,458,084 Lee Jan. 4, 1949 2,459,618- Cartier Ian. 18, 1949 2,465,864Freeman et a1. Mar. 29, 1949 2,541,857 Besselman et a1 Feb. 13, 19512,493,135 Gruetjen Jan. 3, 1950 2,639,138 Dow May 19, 1953 FOREIGNPATENTS 222,575 Great Britain Oct. 6, 1924

1. A HEAT-TREATING FURNACE HAVING A HEATING CHAMBER AND A VESTIBULE FORRECEIVING WORK PREPARATORY TO DELIVERY INTO SAID HEATING CHAMBER, A FANDISPOSED WITHIN SAID HEATING CHAMBER HAVING A HIGH-PRESSURE ZONE FORFORCED CIRCULATION OF GASES WITHIN SAID HEATING CHAMBER, WALLS FORMING AFLOW PASSAGE EXTENDING BETWEEN SAID HEATING CHAMBER AND SAID VESTIBULEWITH AN ENTRANCE PORTION EXTENDING INTO SAID HEATING CHAMBER TO A POINTWITHIN SAID HIGH-PRESSURE ZONE AND ADJACENT SAID FAN PORTION EXTENDINGINTO SAID HEATING CHAMBER TO A POINT FOR FORCED FLOW OF GASES FROM SAIDHEATING CHAMBER INTO SAID VESTIBULE TO FORM THEREIN AN ATMOSPHERE HAVINGSUBSTANTIALLY THE SAME CONSTITUENT QUALITY AS THAT WITHIN SAID HEATINGCHAMBER, AND MEANS INCLUDING A CONSTITUENT-SENSITIVE DEVICE EXPOSED TOTHE ATMOSPHERE OF SAID HEATING CHAMBER FOR CONTROLLING THE CONSTITUENTCONCENTRATION IN SAID HEATING CHAMBER AND OF THE ATMOSPHERE IN SAIDVESTIBULE FORMED BY THE GASES TRANSFERRED THERETO FROM SAID CHAMBER.